JP2016523426A - Improved sintered paste containing partially oxidized metal particles - Google Patents

Abstract

The present invention relates to a sinterable mixture and a method for bonding components using the mixture. The invention further relates to a method for producing a sinterable mixture. [Selection figure] None

Description

  The present invention relates to a sinterable mixture and a method for bonding components using the mixture. The invention further relates to a method for producing a sinterable mixture.

  In power engineering, it is particularly difficult to combine components such as, for example, LEDs with high pressure resistance and high temperature resistance or very thin silicon chips. For this reason, pressure sensitive and temperature sensitive components are often bonded together using an adhesive. However, the bonding technique has the disadvantage that it results in contact sites between components that have poor thermal and / or electrical conductivity. In order to solve this problem, the components to be bonded are often sintered. Sintering technology uses a sintered paste in a very simple way to stably combine the components.

  For example, U.S. Patent No. 6,057,031 uses a sintered paste comprising silver particles coated at least in part with a fatty acid or fatty acid derivative and a volatile dispersant to enhance the sintering process, electrical conductivity, and thermal conductivity. Is described.

  Patent Document 2 discloses a sintered paste containing metal particles, a metal precursor, a solvent, and a sintering aid.

  According to Patent Document 3, at least one aliphatic hydrocarbon compound is added to the sintered paste in order to ensure a low sintering temperature.

  However, despite the use of various sintering aids, it was clear that it was necessary to increase the sinterability of conventional pastes or mixtures, especially at low process pressures.

US Pat. No. 7,766,218 International Publication No. 2011/026624 European Patent No. 2425290

  Within the scope of the present invention, sinterability includes the ability to diffuse a mixture containing metal particles and was used to bond the adhesion at the contact of the mixture.

  Furthermore, at this time, a sinterable mixture was needed that could be used in a wider temperature and pressure range than was feasible. Furthermore, a sinterable mixture with improved diffusivity is desirable, and the use of the mixture increases the adhesion of the sintered contact when used under comparable conditions compared to previous conventional pastes.

  The present invention is therefore based on the object of providing a sintered paste, in particular a sintered paste, which has a high sinterability when applied to the surface of a sinterable mixture, in particular copper. Another object of the present invention is to provide a sinterable mixture in which the sintering process can proceed under milder conditions, mainly at lower temperatures and lower pressures, after which the prior art may be followed. Thus, the use of the mixture requires an energy-saving method for bonding the contacts.

  The object is achieved by the features of the independent claims of the present invention.

Thus, the subject of the present invention is
(A) metal particles;
(B) an organic compound represented by the formula I: R ¹ -COR ² (I),
Wherein R ¹ is an aliphatic residue having 8 to 32 carbon atoms, R ² includes an —OM moiety or —X—R ³ moiety, M is a cation, and X is O, S, An organic compound selected from the group consisting of N—R ⁴ , wherein R ³ is a hydrogen atom or an aliphatic residue, and R ⁴ is a hydrogen atom or an aliphatic residue;
Including
It is a mixture in which the molar ratio of carbon present in the organic compound (b) to oxygen present in the metal particles (a) is in the range of 3-50.

  Furthermore, the present invention provides an alternating stack comprising at least a first component, a second component, and a mixture according to the present invention, wherein the mixture is between the first component and the second component. And a method of bonding at least two components, comprising the steps of:

  The mixture according to the invention can be sintered and is preferably present as a sintered paste, in particular as a printable sintered paste.

  The present invention is based on the surprising research result that the molar ratio of carbon in the organic compound b) to oxygen in the metal particles a) has a great influence on the sinterability of the mixture made from them. It has been surprisingly found that a relatively narrow molar ratio enhances the sintering properties.

Shows very good results of bending test. Showing very poor results of bending tests.

Metal particles (a)
The mixture according to the invention comprises metal particles.

  Within the scope of the present invention, “metal” is the same period as boron, but on the left side of boron, the same period as silicon, but on the left side of silicon, the same period as germanium, but on the left side of germanium, but the same period as antimony. It refers to elements in the periodic system of elements on the left side of antimony and all elements having an atomic number greater than 55. According to the present invention, “metal” also includes alloys and intermetallic phases.

  The purity of the metal is preferably at least 95% by weight, more preferably at least 98% by weight, even more preferably at least 99% by weight, even more preferably at least 99.9% by weight.

  Within the scope of the present invention, the metal particles also include, for example, partially oxidized metal particles whose surface has been oxidized.

  According to a preferred embodiment, the metal is selected from the group consisting of copper, silver, nickel, aluminum, and alloys and mixtures thereof. According to a particularly preferred embodiment, the metal is silver.

  According to another preferred embodiment, the at least one metal of the metal particles (a) is selected from the group consisting of silver, copper, and mixtures thereof.

  The metal of the metal particles (a) preferably consists essentially of silver or copper or a mixture of copper and silver.

  In this context, “essentially” shall mean that at least 95% by weight, in particular at least 97.5% by weight, of the metal particles (a) consist of the corresponding metal or mixture of metals.

  In accordance with the present invention, it is to be understood that the metal alloy is a metal mixture in which at least one of the at least two components is a metal.

  According to a preferred embodiment, the scope of the present invention includes using an alloy comprising copper, aluminum, nickel, and / or a noble metal as the metal alloy. The metal alloy preferably includes at least one metal selected from the group consisting of copper, silver, gold, nickel, palladium, platinum, and aluminum. Particularly preferred metal alloys include at least two metals selected from the group consisting of copper, silver, gold, nickel, palladium, platinum, and aluminum. Further, the proportion of the metal selected from the group consisting of copper, silver, gold, nickel, palladium, platinum, and aluminum is at least 90% by weight of the metal alloy, preferably at least 95% by weight, more preferably at least 99% by weight. %, Even more preferably 100% by weight may be preferred. The alloy may be, for example, an alloy comprising copper and silver, copper, silver and gold, copper and gold, silver and gold, silver and palladium, platinum and palladium, or nickel and palladium.

  The metal particles according to the scope of the present invention may be particles composed of multiple phases. Thus, the metal particles may comprise, for example, a core made of at least one metal phase coated with at least one further metal phase. In this regard, silver-coated copper particles are mentioned for illustration purposes because they are included in the definition of metal particles according to the present invention. In addition, a metal coating may be applied to the non-metallic core. In another embodiment, the metal particles comprise a plurality of different metals. Also preferred are metal particles comprising a metal core made of a non-noble metal and a coating made of a noble metal such as copper particles coated with silver. The mixture according to the present invention may include a pure metal, a plurality of types of pure metals, a type of metal alloy, a plurality of types of metal alloys, or a mixture thereof as a metal. The metal is in particulate form and present in the mixture.

  The metal particles may have different shapes. The metal particles may exist, for example, in a flaky shape or in a spherical shape (ball shape). According to a particularly preferred embodiment, the metal particles take the form of flakes. However, this does not exclude the use of small amounts of differently shaped particles. However, preferably at least 70%, more preferably at least 80%, even more preferably at least 90%, or 100% by weight of the particles are present in the form of flakes.

  The metal particles present in the mixture according to the invention may be of the same or different composition. In particular, the mixture may contain particles made of different metals.

  The mixture according to the invention preferably comprises 60-99.7% by weight, more preferably 77-89% by weight, even more preferably 80-88% by weight of metal particles, based on the total weight of the mixture. With respect to the sinterable mixture according to the invention, the amount of metal particles a) is 96 to 99.7% by weight, preferably 96.5 to 99.%, based on the total weight of metal particles a) and organic compound b). It may be in the range of 5% by weight, more preferably 97 to 99.3% by weight, especially 97.5 to 99.0% by weight.

  Preferably, the metal particles are partially oxidized. Alternatively, there may be a mixture of metal particles in which some of the particles are not oxidized and some of the particles are partially or fully oxidized.

  The oxygen content of the metal particles (a) in the mixture according to the invention is in the range from 0.01 to 0.15% by weight, in particular from 0.05 to 0.10% by weight, based on the total weight of the metal particles. Range.

Measurement of the oxygen content of the metal particles can be performed according to analytical procedures known to those skilled in the art, for example by thermal extraction of the carrier gas using a TC 436 analyzer manufactured by Leco (USA), the oxygen content being is measured indirectly by conversion to _2, CO ₂ gas is detected by the CO ₂ infrared measuring cell. The measurement of oxygen content may be based on the ASTM E1019-03 standard. The adjustment of the device to ensure that the measurement is reproducible is done by inspecting a gas calibration with a known amount of CO ₂ gas and a Leco approved steel standard whose oxygen content is Is approximately the same as the expected oxygen content of the resulting sample. For sample preparation, 100-150 mg of metal powder is weighed into a Leco tin capsule. The sample and tin capsule are then placed in a Leco graphite crucible at 2000 ° C., which has been purged twice beforehand at 2500 ° C. for about 30 seconds each. The sample oxygen reacts with the carbon of the graphite to form carbon monoxide (CO). The carbon monoxide is then oxidized on a Leco copper oxide column (Cu (II) O) to form carbon dioxide (CO ₂ ), where the column has a device-specific temperature of about 600 ° C. The generated carbon dioxide is detected by an infrared cell, whereby the oxygen content of the sample is measured. The blank value for unfilled tin capsules must be measured under the same conditions before the actual measurement of the sample is made. During the actual measurement, the instrument subtracts this blank value from the measured values (tin capsule and sample).

Organic compound (b)
Furthermore, the sintered paste of the present invention contains an organic compound represented by the formula I: R ¹ COR ₂ (I), wherein R ¹ is 8 to 32, preferably 10 to 24, particularly preferably. Is an aliphatic residue having 12 to 18 carbon atoms and may be branched or unbranched. Further, R ¹ may contain a hetero atom. R ² comprises either an —OM moiety or an —X—R ³ moiety, M is a cation, X is selected from the group consisting of O, S, and N—R ⁴ , and R ³ is a hydrogen atom or It is an aliphatic residue, and R ⁴ is a hydrogen atom or an aliphatic residue. In this regard, X is preferably O, N or S, with O being particularly preferred.

Preferably R ³ and / or R ⁴ is an aliphatic residue having 1 to 32, more preferably 10 to 24, in particular 12 to 18 carbon atoms, the residue being linear or branched It may be branched. Furthermore, the residue may also contain one or more heteroatoms. Aliphatic residues may be saturated or unsaturated.

The organic compound is preferably a compound selected from the group consisting of fatty acids (X = O, R ³ = H), fatty acid salts (M = cation), and fatty acid esters.

  Free fatty acids, fatty acid salts, and fatty acid esters are preferably unbranched.

  Furthermore, the free fatty acids, fatty acid salts, and fatty acid esters are preferably saturated.

  According to a preferred embodiment, the organic compound is a fatty monoacid, a fatty monoacid salt, or a fatty monoacid ester.

In a preferred embodiment, the organic compound (b) is a C ₈ -C ₃₀ fatty acid, preferably a C ₈ -C ₂₄ fatty acid, in particular a C ₁₂ -C ₁₈ fatty acid.

  The possible fatty acid salts are preferably such that the anion component is a deprotonated fatty acid and the cation component M is ammonium ion, monoalkylammonium ion, dialkylammonium ion, trialkylammonium ion, lithium ion, sodium ion, potassium ion. , Copper ions, and aluminum ions.

  Preferred fatty acid esters are those derived from the corresponding fatty acid, preferably methyl, ethyl, propyl or butyl esters.

  According to a preferred embodiment, the organic compound comprises caprylic acid (octanoic acid), capric acid (decanoic acid), lauric acid (dodecanoic acid), myristic acid (tetradecanoic acid), palmitic acid (hexadecanoic acid), stearic acid (octadecane). Acid), mixtures thereof, and the corresponding esters and salts, and mixtures thereof.

  According to a particularly preferred embodiment, the organic compound comprises lauric acid (dodecanoic acid), stearic acid (octadecanoic acid), sodium stearate, potassium stearate, aluminum stearate, copper stearate, sodium palmitate, potassium palmitate, And a mixture thereof.

  Furthermore, the organic compound (b) is preferably selected from the group consisting of octanoic acid, stearic acid, lauric acid, palmitic acid, and mixtures thereof.

  For example, a mixture of lauric acid and stearic acid is a particularly preferred mixture. A preferred mixture has a 1: 1 weight ratio of stearic acid to lauric acid as described above.

  Preferably, the organic compound (b) is present in the form of a coating on the metal particles (a).

  Particle coating shall be understood to mean a layer adhered firmly on the surface of the particle. It should be understood that a tightly bonded layer means that it does not separate from the metal particles only by the effect of gravity.

  In this regard, the metal particles used are commercially available. The corresponding organic compound can be applied to the surface of the metal particles by conventional methods known in the prior art.

  For example, the above-mentioned stearic acid and / or lauric acid in a solvent can be slurried, and can be ground with a metal particle in a ball mill. After being powdered, the coated metal particles are dried and then dust is removed.

  Preferably, the proportion of organic compound (b) in the total coating, in particular preferably 8 to 24, more preferably 10 to 24, even more preferably 12 to 18 carbon atoms, free fatty acids, fatty acid salts, Or the proportion of compounds selected from the group consisting of fatty acid esters is at least 60% by weight, more preferably at least 70% by weight, even more preferably at least 80% by weight, even more preferably at least 90% by weight, in particular at least 95% by weight. %, At least 99% or 100% by weight.

  According to a preferred embodiment, the content of the organic compound (b) is 0.1 to 4.0% by weight, more preferably 0.8%, based on the total weight of the particles (a) and the compound (b). 3 to 3.0% by weight, in particular 0.4 to 2.5% by weight, in particular 0.5 to 2.2% by weight, specifically 0.8 to 2.1% by weight. is there.

The degree of coating defined as the mass ratio of the organic compound (b) to the surface of the metal particles (a) is preferably 0.003 to 0.03 g, more preferably 0.003 to 0.03 g, per 1 m ² of the surface of the metal particles. Is 0.007 to 0.02 g, still more preferably 0.01 to 0.015 g.

  According to a preferred embodiment, the mixture according to the invention is 0.05 to 3.5% by weight or 0.08 to 2.5% by weight, more preferably 0.25%, based on the total weight of the mixture according to the invention. -2.2 wt%, even more preferably 0.5-2 wt% of organic compound (b), wherein organic compound (b) is preferably selected from the group consisting of fatty acids, fatty acid salts, and fatty acid esters Is done.

  In a preferred embodiment, the molar ratio of carbon contained in the organic compound (b) and oxygen contained in the metal particles is in the range of 4-45, preferably 5-40, more preferably 10-35, especially 12. -30, specifically, 15-14 is preferable in the range of 15-25 or 12-45.

  Establishing a specific molar ratio of carbon contained in the organic compound (b) and oxygen contained in the metal particles can enhance the sinterability of the paste, which increases the strength of the components bonded together by sintering. It appears in In this regard, the molar ratio at which an improvement in sinterability can be observed is in the range of 3-50, preferably in the range of 4-45. If the molar ratio is out of this specific range, the sinterability cannot be improved. Similarly, the excessive organic compound (b) content adversely affects the applicability of the mixture.

  The carbon content of the organic compound (b) can be calculated from the added amount of the organic compound (b). Alternatively, the carbon content can also be analytically measured by methods known to those skilled in the art, such as elemental analysis, for example according to the ASTM D 529102 standard. The carbon content of the organic compound (b) present in the mixture is determined, for example, by first removing all the carbon-containing compounds of the mixture according to the invention, excluding the organic compound (b) from the mixture, and then the remaining mixture. It can be measured by measuring the carbon content (eg elemental analysis). The carbon-containing compound can also be removed, for example, by heating the mixture for a sufficient time to a temperature below the boiling point of the organic compound (b), but above the boiling point of all other carbon-containing compounds of the mixture. it can.

  Carbon monoxide can be released during the sintering process. Since carbon monoxide is a reducing agent, the metal oxide present on the surface of the metal particles can be reduced. Removing the metal oxide ensures smooth diffusion and reliably improves the diffusivity. The reduction of the metal oxide is also related to the generation of in situ reactive metals that further support the sintering process. Furthermore, the reactive metal can fill the voids between the metal atoms of the metal particles during the sintering process, thus significantly reducing the porosity at the contact sites of the two components to be bonded. The result is a very stable thermal and electrical conductive contact site.

Dispersant (c)
The sinterable mixture according to the invention can be present as a sintered paste and then usually contains an additional dispersant (c). Common dispersants for metal pastes are conceivable for sintered pastes.

  Accordingly, the sinterable mixture of the preferred embodiment of the present invention comprises an additional dispersant (c).

  Within the scope of the present invention, a dispersant shall be understood to mean a substance capable of dissolving and dispersing other substances by physical processes.

  According to the invention, common dispersants for metal pastes are conceivable. Preferably, organic compounds having at least one heteroatom and 6 to 24 carbon atoms, more preferably 8 to 20 carbon atoms, in particular 8 to 14 carbon atoms, are used as dispersants.

  The organic compound may be branched or unbranched. The dispersant (c) is preferably a cyclic compound, in particular a cyclic unsaturated compound.

  Further, the organic compound used as the dispersant may be a saturated, monounsaturated, or polyunsaturated compound.

  The at least one heteroatom contained in the organic compound that can act as a solvent is preferably selected from the group consisting of an oxygen atom and a nitrogen atom.

  At least one heteroatom may be part of at least one functional group.

  According to a particularly preferred embodiment, the dispersant used in this regard is an alcohol.

  For example, monocyclic monoterpene alcohols such as terpineol, especially α-terpineol, are particularly preferred.

  It is particularly preferred that the boiling point of the dispersant is lower than the temperature used to sinter the paste. It is particularly preferred that the boiling temperature of the dispersant is below 240 ° C, more preferably below 230 ° C, especially below 220 ° C.

  In this regard, for example, α-terpineol ((R)-(+)-α-terpineol, (S)-(−)-α-terpineol, or racemate), β-terpineol, γ-terpineol, δ-terpineol, A mixture of these terpineols, N-methyl-2-pyrrolidone, ethylene glycol, dimethylacetamide, 1-tridecanol, 2-tridecanol, 3-tridecanol, 4-tridecanol, 5-tridecanol, 6-tridecanol, isotridecanol, two Using basic esters (preferably dimethyl esters of glutaric acid, dimethyl esters of adipic acid, dimethyl esters of succinic acid, or mixtures thereof), glycerin, diethylene glycol, triethylene glycol, or mixtures thereof Kill.

According to a preferred embodiment, it is preferred to use an aliphatic hydrocarbon compound as a dispersant. In this regard, aliphatic hydrocarbons may be composed of saturated compounds, monounsaturated or polyunsaturated compounds and mixtures thereof. Preferably, the aliphatic hydrocarbon compounds consist of saturated hydrocarbon compounds, which may be cyclic or acyclic, such as n-alkanes, isoalkanes, cycloalkanes, or mixtures thereof. Aliphatic hydrocarbon compounds, for example, may be represented by the formula _{C n H 2n + 2, C} n H 2n, and _C n _{H 2n-2,} n is an integer of 5 to 32. In a particularly preferred embodiment, the aliphatic hydrocarbon compound that can be used as a dispersant is selected from the group consisting of hexadecane, octadecane, isohexadecane, isooctadecane, cyclohexadecane, and cyclooctadecane.

  Dispersant (c) is different from organic compound (b), and in particular, dispersant (c) is not an organic compound included in the definition of organic compound (b).

  The dispersant is usually present in an amount of 6 to 40% by weight, preferably 8 to 25% by weight, in particular 10 to 20% by weight, based on the total weight of the mixture according to the invention.

  The type and amount of the dispersant can be used to adjust the fluidity of the sintered paste. The sintered paste is preferably applied to the component to be sintered by a printing method.

Polymer containing oxygen atom (component (d))
It was surprisingly found that the addition of an organic polymer containing oxygen atoms also increased the sinterability.

  Accordingly, the mixture according to the invention comprises in a preferred embodiment a polymer containing oxygen atoms. Polymers in which oxygen is present are particularly preferred as they are bound as ethers and / or hydroxides. Also preferred are polymers containing alkoxy groups, especially ethoxylate and / or methoxylate groups.

  For example, polysaccharides such as cellulose are preferably polymers that are preferably chemically modified, eg, alkoxylated or alkyl carboxylated.

  Cellulose preferably contains a substitution degree of 2.0 to 2.9, more preferably 2.2 to 2.8. The degree of substitution indicates the average number of chemically modified, in particular etherified, hydroxyl groups per glucose unit. Ethyl cellulose is particularly preferred. Preferably, it has an ethoxy content of 43.0-53.0%, particularly preferably 47.5-50%, in particular 48.0-49.5%, based on the number of hydroxyl groups, and is completely substituted The cellulose has an ethoxy content of 54.88%. Preferably, the viscosity of the cellulose is 60 to 120 cps, more preferably 90 to 115 cps, particularly preferably 85 to 110 cps. In this regard, viscosity was measured according to ASTM D914 using a Hercules Horizontal Capillary viscometer on a mixture consisting of 80% by weight toluene and 20% by weight ethanol.

  Preferably, the cellulose is selected from the group consisting of methylcellulose, ethylcellulose, ethylmethylcellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, or mixtures thereof. Ethyl cellulose is a particularly preferred cellulose.

  The presence of ethyl cellulose further improves paste sinterability through optimized conversion of organic compounds to carbon monoxide.

  Preferably, the mixture according to the invention comprises 0.05 to 2.0% by weight of an oxygen-containing polymer, in particular cellulose, even more preferably 0.1 to 0.8% by weight, based on the total weight of the mixture. Particularly preferably, 0.2 to 0.5% by weight is contained.

Other Raw Material Components Furthermore, the mixture according to the present invention can contain other raw material components such as customary surfactants, antifoaming agents, binders, or viscosity modifiers. Preferably, the mixture can include a wetting agent.

  The other raw material components are usually added in an amount of up to 0.01% by weight, preferably 0.001 to 0.01% by weight, based on the total weight of the mixture according to the present invention.

  Preferably, the mixture according to the invention is essentially free of glass, in particular glass frit. Glass formers such as lead oxide, bismuth oxide, alkali and alkaline earth oxides, tellurium oxide are typical raw material components of glass frit.

  In this context essentially means that the mixture comprises less than 2% by weight of glass and / or glass frit, preferably less than 1% by weight, more preferably less than 0.5% by weight, in particular 0.1% by weight. Less than, specifically less than 0.05% by weight, for example 0% by weight, each specified weight being intended to be relative to the total weight of the mixture.

  In a particular embodiment, the metal particles a) of the sinterable mixture according to the invention are silver particles. The optimum sinterability is that the oxygen content of the silver relative to the organic compound (b) is perfectly compatible with each other (for example by selecting partially oxidized silver and / or a mixture of silver and silver oxide). In some cases, it was surprisingly clear that it could be achieved. In a preferred embodiment, the molar ratio of all oxygen present in the silver particles and organic compound (b) to silver is about 1.0 to about 3.5, preferably about 1.2 to about 3.0, especially about 2.0 to about 2.7.

  Further, the molar ratio of all carbon present in the organic compound (b) to silver is in the range of about 5 to about 20, more preferably about 7 to about 16, especially about 10 to about 15.

  Furthermore, good sinterability results show that the composition of the mixture according to the invention is all oxygen present in the metal particles (a), in particular silver particles, and organic compounds (b), of carbon present in the organic compounds (b). This can be achieved when the molar ratio to is suitably selected to be appropriately adjusted to be in the range of about 200 to about 600, more preferably about 400 to about 570, especially about 500 to about 550.

In a preferred embodiment, the mixture according to the invention is
(A) preferably 75 to 90% by weight of metal particles, preferably silver, selected from the group consisting of silver, copper, aluminum and nickel;
(B) preferably 0.05 to 3.0% by weight, preferably selected from the group consisting of fatty acids, fatty acid salts and fatty acid esters, in particular of fatty acids, more preferably present as a coating on metal particles (a) An organic compound (b) of
(C) 6 to 30% by weight of a dispersant, preferably selected from the group of alcohols, in particular terpineol;
(D) if applicable, containing 0.05-1.0% by weight of cellulose, in particular ethylcellulose,
The molar ratio of carbon contained in the organic compound (b) to oxygen contained in the metal particles (a) is in the range of 5 to 40, preferably 10 to 35, more preferably 12 to 30, particularly preferably 15 to 25. These specified weights each relate to the total weight of the sinterable mixture.

Sintering One of the subjects of the invention is also a method for producing a mixture according to the invention, in which the metal particles (a), the organic compound (b) and, if applicable, the dispersant (c) are mixed.

  According to a preferred refinement of the invention, the mixing of the metal particles (a) and the organic compound (b) is carried out in such a way that the organic compound (b) is slurried in a solvent and the metal particles (a ). Thereafter, if applicable, the coated metal particles may then be dried and dust removed in a further step.

  The sinterable mixture according to the invention can be produced with mixing equipment and agitators well known to those skilled in the art. In a preferred refinement of the production method according to the invention, the metal particles are coated with the organic compound (b) in the first step. The coated particles are mixed with the dispersant (c) in the next step.

  According to the invention, the paste according to the invention is used in a sintering process.

  Preferably, it should be understood that sintering means that two or more components are combined by heating without producing a liquid phase. Thus, sintering proceeds as a diffusion process.

  According to the present invention, it should be understood that combining at least two components means combining a first component onto a second component. In this context, “on” simply means that the surface of the first component is bonded to the surface of the second component, regardless of the relative arrangement of the two components or an arrangement comprising at least two components.

  Within the scope of the present invention, a component preferably includes a single component. In particular, the single component cannot be further disassembled.

  A component within the scope of the present invention may be any object independent of function. In this regard, the terms component, component, and substrate are considered synonymous within the scope of the present invention.

  According to a particular embodiment, the component is an object comprising at least one metal surface.

  According to certain embodiments, a component refers to a component used in high performance electronics.

  Thus, the components are, for example, diodes, LEDs (light emitting diodes), DCB (direct copper junction) substrates, lead frames, dies, IGBTs (insulated gate bipolar transistors, bipolar transistors), IC (integrated circuits). , Integrator Schaltungen), sensors, heat sink elements (preferably aluminum heat sink elements or copper heat sink elements) or other passive elements (eg resistors, capacitors or coils). Preferably, the component may be a non-metallic component.

  The components to be combined may be the same or different components.

  Preferred embodiments of the present invention include LED to lead frame, LED to ceramic substrate, die, diode, IGBT or IC to lead frame, ceramic substrate or DCB substrate, sensor to lead frame or ceramic substrate, DCB or ceramic. It relates to bonding a substrate to a copper or aluminum heat sink element, a lead frame to a heat sink element, or preferably an unstored tantalum capacitor to the lead frame.

  It is also preferred to combine more than two components together. For example, (i) an LED or chip can be coupled to (ii) a lead frame and (iii) a heat sink element, and the lead frame is preferably located between (i) the LED or chip and (iii) the heat sink element. . A diode may also be coupled to the two heat sink elements, and the diode is preferably located between the two heat sink elements.

  According to a preferred embodiment, the component can comprise at least one metal surface. The metal surface is preferably part of the component. Preferably, the metal surface is located on at least one surface of the component.

  The metal surface may include pure metal. Thus, the metal surface may preferably comprise at least 50 wt%, more preferably at least 70 wt%, even more preferably at least 90 wt% or 100 wt% pure metal. Preferably, the pure metal is selected from the group consisting of aluminum, copper, silver, gold, palladium, and platinum.

  On the other hand, the metal surface may also comprise an alloy. The metal surface alloy preferably comprises at least one metal selected from the group consisting of silver, gold, nickel, palladium, and platinum. It may be preferred that the metal surface alloy also includes at least two metals selected from the group consisting of silver, gold, nickel, palladium, and platinum. The proportion of the alloy occupied by an element selected from the group consisting of silver, gold, nickel, palladium and platinum is preferably at least 90% by weight, more preferably at least 95% by weight, even more preferably at least 99% by weight, for example 100% by weight.

  According to a preferred embodiment, the metal surface preferably comprises at least 95% by weight, more preferably at least 99% by weight, and even more preferably 100% by weight of the alloy. The metal surface may have a multilayer structure. Thus, it may be preferred that at least one surface of the components to be combined comprises a metal surface consisting of multiple layers comprising the pure metals and / or alloys described above.

  According to a preferred embodiment, the component, in particular the at least one metal surface of the DCB substrate, comprises a layer made of copper, on which a layer made of nickel is applied. Where applicable, a further layer made of gold may be applied over the layer made of nickel. In this case, the thickness of the layer made of nickel is preferably 1 to 2 μm, and the thickness of the layer made of gold is preferably 0.05 to 0.3 μm. On the other hand, it may be preferred that the metal surface of the component includes a layer made of silver or gold and further includes a layer made of palladium or platinum.

  According to a further preferred embodiment, each layer also contains glass in addition to certain pure metals or alloys. These layers may preferably be a mixture of (i) glass and (ii) pure metal or alloy.

  According to the invention, at least two components are bonded together by sintering.

  For this purpose, at least two components are first brought into contact with each other. In this connection, the contact is achieved by the metal paste according to the invention. For this, an arrangement is provided, in which the metal paste is located between each two of the at least two components.

  Thus, if the two components, ie component 1 and component 2, are bonded together, the metal paste according to the invention is positioned between component 1 and component 2 before the sintering process. On the other hand, it is also conceivable to combine more than two components together. For example, three components, component 1, component 2, and component 3, may be suitably coupled together such that component 2 is located between component 1 and component 3. In this case, the metal paste according to the invention is located both between component 1 and component 2 and between component 2 and component 3. The present invention places the components in an alternating arrangement and combines them together.

  According to the present invention, an alternating arrangement is to be understood as meaning an arrangement in which the two components are located one above the other and the contact surfaces to be joined are located essentially parallel to each other.

A further aspect of the present invention is a method for combining at least two components, comprising the following steps.
Providing an alternating stack comprising at least a first component, a second component, and a mixture according to the invention, wherein the mixture is positioned between the first component and the second component, and alternating Sintering the stacking arrangement.

  The arrangement of the at least two components and the metal paste may be generated by any method known from the prior art where the metal paste is positioned between the two components of this arrangement.

  Preferably, first, the metal paste according to the present invention is supplied to at least one surface of component 1. Next, another component 2 is placed by one of its surfaces onto the metal paste applied to the surface of component 1.

  According to a preferred embodiment of the method, at least one of the components has a metal surface, preferably a gold surface, a palladium surface, a silver surface or a copper surface on which according to the invention. A mixture is applied.

Also preferred is an embodiment of the method comprising the following steps.
a) applying the mixture according to the invention to the component surfaces of the components;
b) providing an alternating arrangement by appropriately positioning the second component such that the mixture is located between the first component and the second component;
c) Sintering the alternating stack arrangement.

  One embodiment is particularly preferred in which at least one of the component surfaces to which the mixture is applied is a non-noble metal surface, in particular copper.

  In particular, when one of the component surfaces to be bonded includes a non-noble metal surface, particularly copper, the molar ratio of carbon contained in the organic compound (b) to oxygen contained in the metal particles (a) is in the range of 11 to 48. It has surprisingly been found that 14 to 40 mixtures according to the invention are advantageous. It has also been found that sintering at low process pressures, for example 0 Mpa, is feasible, especially at this molar ratio.

  Application of the metal paste components to the surface can be accomplished by any conventional method. Preferably, the metal paste is applied using a printing method, for example by screen printing or stencil printing. However, the metal paste may be applied by dispensing technology, spray technology, spray technology, pin transfer, or immersion.

  After application of the metal paste, it is preferable to bring the surface of the component comprising the metal paste into contact with the surface of the component that is bound to it by the metal paste. Thus, the layer of metal paste is located between the components to be combined.

  Preferably, the wet layer thickness between the components to be combined is in the range of 15-200 μm. In this regard, the wet layer thickness shall be understood to mean the distance between the opposing surfaces of the components to be combined prior to the sintering process. The preferred thickness of the wet layer depends on the method selected for applying the metal paste. When the metal paste is applied, for example by screen printing, the wet layer thickness may preferably be 15-50 μm. When the metal paste is applied by stencil printing, the preferred thickness of the wet layer may be in the range of 50-200 μm. According to a preferred embodiment, the drying step is performed before the sintering process.

  Preferably, it should be understood that drying means reducing the proportion of dispersant in the metal paste.

  Drying may take place after creation of the arrangement, i.e. after contacting the components to be combined. However, drying may also take place immediately after the metal paste is applied on at least one surface of the components and before contact with the components to be combined.

  Preferably, the drying temperature is in the range of 50-160 ° C.

  Obviously, the drying time depends on the specific composition of the metal paste and the size of the arrangement to be sintered. Typical drying times range from 5 to 45 minutes.

  The arrangement consisting of at least two components and a metal paste located between the two components is finally subjected to a sintering process.

In this regard, the component dimensions may vary, preferably from about 0.5 mm ^{2 to} 180 cm ^2, with the preferred component being rectangular or circular.

  The sintering process is preferably performed at 180 ° C. or lower, 250 ° C. or lower, particularly 200 ° C. to 240 ° C.

  In this regard, the process pressure is preferably in the range of 30 Mpa or less and 0 Mpa or more, and more preferably in the range of 5 Mpa to 25 Mpa. However, the sintering process may be carried out without applying process pressure, i.e. at a process pressure of 0 Mpa. The sintering time is preferably in the range of 2 to 60 minutes depending on the process pressure.

  The sintering process may be performed in an atmosphere without any limitation. Preferably, however, the sintering process is performed in an oxygen containing atmosphere.

  The sintering process is performed in a conventional apparatus suitable for sintering in which the process parameters described above can be preferably set.

  The present invention is illustrated by the examples described below, which are not to be construed as limiting the invention in any way or form.

Production of Metal Paste First, metal pastes 1 to 13 were produced by mixing raw material components in the quantitative ratios shown in Table 1.

  A mixture of stearic acid and lauric acid was used as a coating in a mass ratio of 75:25.

  Partially oxidized silver particles (D50: 4 μm) were used as metal particles.

  α-Terpineol or a mixture of 1: 1 α-terpineol and tridecanol was used as a dispersant.

  In Examples 6, 8, and 10, additional cellulose (degree of substitution: 100) was added to the paste.

Paste Application and Sintering Procedure The paste was applied by stencil printing at 20-25 ° C., the stencil was 75 μm thick and the printing area was 10 × 10 mm. A steel squeegee with a pitch angle of 60 degrees was used. The printing speed was 50 mm / s.

  The resulting metal paste was used to sinter the two components bonded together.

  The sinterability (see Table 2) of the different sinterable mixtures (Table 1) was measured by two sintering procedures: pressure sintering and pressureless sintering. The sintering conditions are as follows.

a) Pressure Sintering Pressure sintering was performed after applying the sintered paste to the component containing the gold / nickel surface (the sintered paste was in contact with the gold side) or after applying it to the copper surface. The sintered paste was then contacted with a silicon component having a TiNiAg metal coating and sintered at 240 ° C. for 3 minutes at the respective pressure (process pressure).

b) Pressureless sintering Pressureless sintering was performed after applying the sintered paste to the component containing the gold / nickel surface (the sintered paste was in contact with the gold side) or after applying it to the copper surface. . The sintered paste was then contacted with a silicon component having a TiNiAg metal coating. The following heating profile was used for pressureless sintering. The sintered contact sites were gradually heated at 25 ° C. to 160 ° C. over 30 minutes and then maintained at 160 ° C. for 30 minutes. The temperature was then gradually increased to a final temperature of 230 ° C. over 5 minutes and then maintained at this temperature for 60 minutes. Thereafter, the temperature was gradually lowered to 30 ° C. over 50 minutes.

  The sintering process may proceed under a protective gas atmosphere (nitrogen) or exposed to air.

Sinterability evaluation Sinterability was measured according to two equally weighted evaluation criteria.

First Criteria: Screen Cut Test The sintered contact site had 5 parallel cut lines in the horizontal and vertical directions. The length between each cut line was 1 mm.

  If the sintered layers do not separate and the cut is clean, a very good screen cut (grade = 1) is evident.

  A moderate screen cut (grade = 3) is evident when there is a slight detachment and breakage.

  If the sintered layers separate, a very poor screen cut (grade = 5) is evident.

  A good screen cut (grade = 2) is evident if the screen cut is between a very good screen cut and a moderate screen cut.

  If the screen cut is between a moderate and very poor screen cut, a poor screen cut (grade = 4) is evident.

Second Criteria: Bending Test A substrate bonded to the silicon component was attached to a roller as shown in FIGS. 1 and 2, a silicon component (3) sintered against a substrate (nickel / gold component or copper component) (1) by a sintered layer (4) is attached to a roller (2) with a diameter of 2 cm. . The composite was advanced from right to left and bent on a roller. FIG. 1 shows a bending test with very good results (grade = 1) since the silicon component (3) is completely adhered to the substrate.

  FIG. 2 shows a bending test with very poor results (grade = 5) because the silicon component (3) is peeled off the substrate. Grades 2-4 are between these extremes.

  Thereafter, the grades of the screen cut test and the bending test were added, and the average value was calculated. The average value is shown as “sinterability” in Table 2 for each sinterable mixture.

The sinterability results for each paste are shown in Table 2.

Claims (19)

(A) metal particles;
(B) an organic compound represented by the formula I: R ¹ -COR ² (I),
Wherein R ¹ is an aliphatic residue having 8 to 32 carbon atoms, R ² includes an —OM moiety or —X—R ³ moiety, M is a cation, and X is O, S, An organic compound selected from the group consisting of N—R ⁴ , wherein R ³ is a hydrogen atom or an aliphatic residue, and R ⁴ is a hydrogen atom or an aliphatic residue;
Including
A mixture in which the molar ratio of carbon present in the organic compound (b) to oxygen present in the metal particles (a) is in the range of 3-50.   The mixture of claim 1, wherein the at least one metal of the metal particles (a) is selected from the group consisting of silver, copper, nickel, aluminum, alloys, and mixtures thereof.   The mixture of claim 1 or 2, wherein the at least one metal of the metal particles (a) is selected from the group consisting of silver, copper, and a mixture of copper and silver. Organic compound (b) _is a fatty acid of C 8 _{-C 30,} preferably fatty acids _C 8 _{-C 24,} more preferably a fatty acid of _C 12 _{-C 18,} any one of the preceding claims The mixture described in 1.   The mixture according to any one of claims 1 to 4, wherein the organic compound (b) is selected from the group consisting of octanoic acid, stearic acid, lauric acid, palmitic acid, and mixtures thereof.   6. A mixture according to any one of the preceding claims, wherein the paste comprises an additional polymer comprising oxygen atoms.   The mixture according to any one of claims 1 to 6, wherein the organic compound (b) is present in the form of a coating on the particles (a).   Compound (b) is present in an amount of 0.1-4.0% by weight, more preferably 0.3-3.0% by weight, based on the total weight of particles (a) and compound (b). Even more preferably from 0.4 to 2.5% by weight, particularly preferably from 0.5 to 2.2% by weight, in particular from 0.8 to 2.0% by weight. The mixture according to any one of the above.   The metal particles (a) have an oxygen content of 0.01 to 015% by weight, preferably 0.05 to 0.10% by weight, based on the weight of the metal particles (a). The mixture according to any one of claims 1 to 8.   The molar ratio of carbon contained in the organic compound (b) to oxygen contained in the metal particles is 4-45, preferably 5-40, more preferably 10-35, especially 12-30, specifically 15-25. Or the mixture according to any one of claims 1 to 9, wherein 15 to 14 is preferred in the range of 12 to 45.   (C) The mixture according to any one of claims 1 to 10, further comprising a dispersant.   The dispersant (c) is α-terpineol, β-terpineol, γ-terpineol, δ-terpineol, a mixture of the above-mentioned terpineols, N-methyl-2-pyrrolidone, ethylene glycol, dimethylacetamide, 1-tridecanol, 2-tridecanol. 3-tridecanol, 4-tridecanol, 5-tridecanol, 6-tridecanol, isotridecanol, dibasic ester, preferably dimethyl ester of glutaric acid, dimethyl ester of adipic acid, dimethyl ester of succinic acid, or 12. The mixture of claim 11 selected from the group consisting of a mixture, glycerin, diethylene glycol, triethylene glycol, and mixtures thereof.   The method for producing a mixture according to any one of claims 1 to 10, wherein the metal particles (a), the organic compound (b), and, if applicable, the dispersant (c) are mixed. . A step of providing an alternating stack comprising at least a first component, a second component, and a mixture according to any one of claims 1 to 12, wherein the mixture is combined with the first component and the first component. Positioning between the second component;
Sintering the alternating arrangement;
A method of combining at least two components comprising:   The bonding method according to claim 14, wherein the sintering step is performed at a temperature of 180 ° C to 250 ° C, preferably at a temperature of 200 ° C to 240 ° C.   The bonding method according to claim 14 or 15, wherein the sintering is performed at a process pressure of 0 MPa to 30 MPa, preferably at a process pressure of 5 MPa to 25 MPa.   17. At least one of the components has a metal surface, preferably a gold surface, a palladium surface, a silver surface, or a copper surface, on which the mixture is applied. The bonding method according to any one of the above. a) applying the mixture according to any one of claims 1 to 12 to the component surface of the first component;
b) providing an alternating arrangement by appropriately arranging the second component such that the mixture is located between the first and second components;
c) sintering the alternating stack arrangement;
The coupling | bonding method of any one of Claims 14-17 containing this. The bonding method according to any one of claims 14 to 18, characterized in that at least one of the surfaces of the component to which the mixture is applied is a non-noble metal surface, in particular copper.

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